I guess you want to have something like http://ez.no/content/view/sitemap
Just create a link to www.yourdomain.com/content/view/sitemap and eZ publish templating system will do the rest.
If you want a sitemap from another node than the main node (like the sitemap of a subset of your portal) just have the link like www.yourdomain.com/content/view/sitemap/128 and you have the sitemap of whatever content below that node.
By the way, in ezwebin package, the link to the sitemap is by default on top of each page.